Merge branch 'llvm6'

Zig now depends on LLVM 6.0.0.

The latest commit that depends on LLVM 5.0.1 is
2e010c60ae006944ae20ab8b3445598471c9f1e8.
3200ebc2eaAndrew Kelley committed on 3/8/2018, 3:59:54 PMparents2e010c6b57cb04
64 files changedLine totals unavailable